Interpretive Summary: Reliable data on the environmental factors which affect the transfer of disease causing microorganisms, such as Giardia and Cryptosporidium (oo)cysts, from animal manure to water are needed to accurately assess and minimize contamination potential to surface and drinking water supplies. Studies were initiated to determine the influence of various physical factors (water application method, flow rate, manure type, temperature) on the transfer behavior of naturally occurring (oo)cysts from Holstein dairy calf manure to water. Higher concentrations of (oo)cysts occurred when water was applied as drips compared to a mist, and for higher water flow rates. Temperature did not significantly influence (oo)cyst concentrations. Increasing the cow manure fraction of the a manure mixture tended to decrease the manure concentration in the water, but also increased the (oo)cyst numbers relative to the dissolved manure concentration. A conceptual model to predict the release behavior of manure and (oo)cysts was successfully applied to the experimental data.

Technical Abstract:
Reliable data on the environmental factors that affect the transfer of disease causing Cryptosporidium and Giardia (oo)cysts from animal manure to water are needed to accurately assess and minimize contamination potential to surface and groundwater resources. Studies were therefore initiated to determine the influence of various physical factors on the release rate of naturally occurring (oo)cysts from dairy manure disks to sprinkled water. The variables that were investigated include water application method (aerosol or drip) and flow rate, manure type (calf manure, and 1:1 and 1:10 ratios of cow and calf manure) and temperature (5 or 23 deg. C). Effluent concentrations of manure and (oo)cysts in the runoff water were initially several orders of magnitude below their starting concentration in the manure, then decreased gradually and exhibited persistent concentration tailing. A strong linear relation between the release of manure and (oo)cysts was found, and the efficiency of (oo)cyst release relative to manure release was calculated. A conceptual model was applied to describe manure release. The inclusion of (oo)cyst release efficiencies into this model provided a satisfactory simulation of the observed (oo)cyst release behavior. In comparison to aerosol application, dripping water resulted in higher release rates of manure and (oo)cysts and in higher (oo)cyst release efficiencies. These differences were attributed to the increased physical forces associated with droplet impact. Aerosol application at a higher flow rate resulted in faster release, but did not affect the (oo)cyst release efficiencies. The manure and (oo)cyst release rates from cow manure decreased faster than that from calf manure, and (oo)cyst release efficiencies from cow manure were higher. An effect of temperature on the release of manure and (oo)cysts was not apparent. The data and modeling approach described herein provide insight and an enhanced ability to describe the influence of physical factors on (oo)cyst release.